/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

package org.apache.tomcat.jni;

import java.nio.ByteBuffer;

/**
 * Shm
 * 
 * @author Mladen Turk
 * @version $Revision: 467222 $, $Date: 2006-10-24 11:17:11 +0800 (星期二, 24 十月
 *          2006) $
 */

public class Shm {

	/**
	 * Create and make accessable a shared memory segment. <br />
	 * A note about Anonymous vs. Named shared memory segments:<br />
	 * Not all plaforms support anonymous shared memory segments, but in some
	 * cases it is prefered over other types of shared memory implementations.
	 * Passing a NULL 'file' parameter to this function will cause the subsystem
	 * to use anonymous shared memory segments. If such a system is not
	 * available, APR_ENOTIMPL is returned. <br />
	 * A note about allocation sizes:<br />
	 * On some platforms it is necessary to store some metainformation about the
	 * segment within the actual segment. In order to supply the caller with the
	 * requested size it may be necessary for the implementation to request a
	 * slightly greater segment length from the subsystem. In all cases, the
	 * apr_shm_baseaddr_get() function will return the first usable byte of
	 * memory.
	 * 
	 * @param reqsize
	 *            The desired size of the segment.
	 * @param filename
	 *            The file to use for shared memory on platforms that require
	 *            it.
	 * @param pool
	 *            the pool from which to allocate the shared memory structure.
	 * @return The created shared memory structure.
	 * 
	 */
	public static native long create(long reqsize, String filename, long pool)
			throws Error;

	/**
	 * Remove shared memory segment associated with a filename. <br />
	 * This function is only supported on platforms which support name-based
	 * shared memory segments, and will return APR_ENOTIMPL on platforms without
	 * such support.
	 * 
	 * @param filename
	 *            The filename associated with shared-memory segment which needs
	 *            to be removed
	 * @param pool
	 *            The pool used for file operations
	 */
	public static native int remove(String filename, long pool);

	/**
	 * Destroy a shared memory segment and associated memory.
	 * 
	 * @param m
	 *            The shared memory segment structure to destroy.
	 */
	public static native int destroy(long m);

	/**
	 * Attach to a shared memory segment that was created by another process.
	 * 
	 * @param filename
	 *            The file used to create the original segment. (This MUST match
	 *            the original filename.)
	 * @param pool
	 *            the pool from which to allocate the shared memory structure
	 *            for this process.
	 * @return The created shared memory structure.
	 */
	public static native long attach(String filename, long pool) throws Error;

	/**
	 * Detach from a shared memory segment without destroying it.
	 * 
	 * @param m
	 *            The shared memory structure representing the segment to detach
	 *            from.
	 */
	public static native int detach(long m);

	/**
	 * Retrieve the base address of the shared memory segment. NOTE: This
	 * address is only usable within the callers address space, since this API
	 * does not guarantee that other attaching processes will maintain the same
	 * address mapping.
	 * 
	 * @param m
	 *            The shared memory segment from which to retrieve the base
	 *            address.
	 * @return address, aligned by APR_ALIGN_DEFAULT.
	 */
	public static native long baseaddr(long m);

	/**
	 * Retrieve the length of a shared memory segment in bytes.
	 * 
	 * @param m
	 *            The shared memory segment from which to retrieve the segment
	 *            length.
	 */
	public static native long size(long m);

	/**
	 * Retrieve new ByteBuffer base address of the shared memory segment. NOTE:
	 * This address is only usable within the callers address space, since this
	 * API does not guarantee that other attaching processes will maintain the
	 * same address mapping.
	 * 
	 * @param m
	 *            The shared memory segment from which to retrieve the base
	 *            address.
	 * @return address, aligned by APR_ALIGN_DEFAULT.
	 */
	public static native ByteBuffer buffer(long m);

}
